Coseismic Vertical Displacement and Fault Motion Model of the Nepal Mw7.9 Earthquake

The 2015 Nepal Mw7.9 earthquake occurred in the central segment of the Himalayan collision zone, where the rigid Indian plate thrusts beneath the Tibetan Plateau. The published focal mechanism solution shows this earthquake was dominated by thrust slip but minor right-lateral strike slip, so a significant vertical deformation appears on the surface caused by this event. Accurate coseismic vertical displacements in this region provide us a scarce chance to understand the long term uplift of the Himalaya and southern Tibet. By processing the resurvey 'in-situ' GPS data, we obtained a coseismic GPS horizontal displacement field at high precision. In combination with the coseismic GPS displacements and the L-band InSAR line of sight (LOS) observations, we extract the coseismic vertical deformation field due to the Nepal earthquake with a mean uncertainty of 1~2 cm and spatial resolution of 1 km×1 km. The result shows that the Kathmandu was uplifted ~0.95 m after the main shock. In particular, the Mount Everest and Shishapangma subsided~2-3 cm and ~20 cm, respectively. The two-dimensional elastic half-space dislocation model suggests that the mean rupture width of the Nepal earthquake was~60 km and the average coseismic slip reached 4 m. Our results indicate that the slip deficit of this event was equivalent to a moment magnitude of Mw 7.89 assuming a rupture length of 120 km and rigidity of 30 GPa, which is consistent with seismological estimation.The 2015 Nepal earthquake broke the trend of long term uplift in the central segment of higher Himalaya during an interseismic period. Whether this segment will continue to subside or uplift after the event can be discriminated by continuous post-seismic geodetic measurements.